This invention relates to an apparatus for forming flexible fold lines in a sheet of thermoplastic material and is particularly useful in making foldable box blanks. In this art, heat is applied to the thermoplastic sheet so that it is partially softened, and the thermoplastic sheet is deformed between two tools. During the forming process, fold lines or crease lines are formed in the thermoplastic sheet, and this makes it possible to bend the sheet about the fold line to form the blank into a box. It is desirable that such fold lines have no memory in returning to their flat configuration from a folded position.
There are a number of relevant prior art patents in this field. For example, U.S. Pat. No. 4,179,252 relates to an apparatus for forming flexible fold lines in a thermoplastic sheet. Such apparatus employs a high-frequency generator for creating a high-frequency electric field between an upper tool and a flat plate, so that the high-frequency electric field provides sufficient het to soften the thermoplastic sheet.
The drawbacks of such prior arrangements are that a costly high-frequency generator is required to heat the thermoplastic sheet, as well as cooling apparatus to cool the scoring tools. Such drawbacks hve been overcome by the present invention, since such costly apparatus is not required to form foldable boxes having flexible fold lines.
Broadly, it is an object of the present invention to provide an improved apparatus for forming plastic box blanks which overcomes the drawbacks of the prior art. Specifically, it is within the comtemplation of the present invention to provide an apparatus which is inexpensive, efficient, and provides a quality product.
It is a further object of the present invention to provide an apparatus which includes a grooved plate for receiving plastic within its grooves along the fold lines to form a plastic sheet having fold lines which include thick and thin areas for increased strength and flexibility.